In surveying of object representing points in general a perpendicular pole, also known as range pole or surveying pole, is employed. A perpendicular pole is a pole used for surveying and having a reflector on its top end. The reflector serves for reflecting beams such as laser beams or light beams emitted from a surveying instrument or another source, back to the surveying instrument. The perpendicular pole is placed vertically right on the point to be surveyed, and then a horizontal angle, a vertical angle as well as the distance from the used surveying instrument such as a total station to a reflector mounted on top of the perpendicular pole is measured. The base point is then derived by subtracting the vertical height from the measured coordinates.
This method, however, can be employed only, if the perpendicular pole can be placed directly and vertically on the point. Therefore, this method cannot be directly employed if for instance the object representing point is the basis point of a building corner, the central point of a pole, mast, tree etc.
In such cases, in a first step the perpendicular pole is to be placed adjacent to the object to be surveyed. FIGS. 1a and 1b show an example for measuring a corner of a house. Here, the distance from a total station 1 used as surveying instrument to a reflector on top of the perpendicular pole 2 more or less corresponds to the distance of the corner 3 of the house to be surveyed. In a second step the total station 1 is collimated with the corner of the house and the horizontal angle as well as the vertical angle is measured. On the basis of the angle and distance measurements the coordinates of the object representing point are computed.
Another example where a mast is surveyed is shown in FIGS. 1c and 1d. Here, for the determination of the distance the perpendicular pole 2 is also placed adjacent to the mast. The measured distance from the total station to the reflector on top of the perpendicular pole 2 more or less corresponds to the distance from the used total station to the centre point 4 of the mast. For the angle measurement the total station 1 is collimated with the centre of the mast. On the basis of the angle and distance measurements the coordinates of the object representing point are computed.
As can be gathered from the FIGS. 1a to 1d as well as from the above explanation, problems with this surveying method may occur. Firstly, a plurality of manual steps is to be performed in order to obtain a surveying result. This has negative effects on the productivity. Secondly, due to inaccuracies when placing the perpendicular pole 2 and the reflector, respectively, the accuracy of the obtained surveying results is limited. Therefore, the reliability of the obtained surveying results cannot be fully ensured.
A possible solution would be to perform a reflector-less measurement directly to the edge of the object. The edge of the object is to be understood as the edge of a house wall corner. However, as can be seen from FIG. 2a, this method is neither fully reliable. As shown in FIG. 2a, a portion 5b of the measuring beam 5 (e.g. a laser beam) might pass the respective edge while another portion 5a is reflected from the wall forming the edge. This leads to a confusing result of the distance measurement and the exact object representing point data cannot be obtained either.
Document EP 1 460 377 A2 discloses a method for surveying an object. Here, a surveying instrument is directed to an object to be surveyed and an image is captured by an integrated camera. From a plurality of templates, a user may select the one corresponding to the surveyed object. Via image processing methods the template is identified in the captured image and based on the result, the object representing point is identified. Furthermore, a distance between the surveying instrument and the object to be surveyed is determined.
With the method disclosed in EP 1 460 377 A2, a plurality of operating steps is to be carried out by the user. Thus, in order to increase productivity, there is need for an optimized surveying method capable to determine the shape and type of a surveyed object in an automated manner.